1. Technical Field
The present invention relates to a radiological image detection apparatus and a radiographic imaging cassette used in a X-ray imaging system, or the like.
2. Related Art
DR (Digital Radiography) using a radiological image detection apparatus, like an FPD (Flat Panel Detector) that converts a radiological image, such as an X-ray image, into digital data, has recently been put into practice. When compared with a related art CR (Computed Radiography) system that uses an imaging plate made of a photostimulable phosphor (an accumulative phosphor), the radiological image detection apparatus has an advantage of being able to ascertain an image immediately. Thus, the DR has become proliferated rapidly.
Various types of radiological image detection apparatuses have already been put forward. One of the radiological image detection apparatuses is of a known indirect conversion type. This type of radiological image detection apparatus temporarily converts X-radiation into visible light by means of a scintillator, like a CsI:Tl scintillator and a GOS (Gd2O2S:Tb) scintillator, and a semiconductor layer converts the visible light into electric charges and accumulates the resultant electric charges (see; for instance, Patent Document 1 (JP-A-2011-17683)).
In the X-ray image detection apparatus described in connection with Patent Document 1, X radiation is emitted from a photodetecting unit to the scintillator. Specifically, the photodetecting unit is disposed on a side of the scintillator facing a subject (a patient), and a light detector is disposed opposite a back side of a support member that supports the subject. Also, as described in Patent Document 1, a panel made up of the light detector and the scintillator can be affixed directly to the support member. However, where the support member and the panel are affixed together, attention must be paid in such a way that the support member can easily be replaced.
Moreover, where a main body of the X-ray image detection apparatus is accommodated in a housing, to thus be formed as a cassette, the light detector opposes a back side of a ceiling of the housing. The cassette is made slim by means of affixing the thus-positioned light detector directly to the ceiling.
In a configuration where the light detector is placed on an X radiation entrance side (i.e., a subject side) of the scintillator like that mentioned above, a short distance lies between a principal light emission area on the X radiation entrance side and the photodetecting unit of the scintillator, a high definition detected image is acquired. In the meantime, a substrate of the photodetecting unit placed on the X radiation entrance side of the scintillator unavoidably absorbs X radiation. Therefore, there is a drawback of the amount of X radiation incident on the scintillator being reduced as a result of X radiation being absorbed by the substrate.
The photodetecting unit is built by inclusion of a photodiode (PD) and a TFT (Thin Film Transistor) that each are formed from a-Si, or the like. Alkali-free glass is usually used for a substrate supporting the PD and the TFT. The reason for this is that, when soda glass is used, a-Si may be contaminated with Na that will stem from glass during formation of an a-Si film in the presence of high temperature, which may in turn deteriorate performance of an element. However, alkali-free glass is more expensive than soda glass and also absorbs a larger amount of X radiation than does the soda glass. For instance, when an X-ray shaped beam generated at a tube voltage of 50 kV is used by applying a filter having 2 mm aluminum equivalent to the photodetecting unit, an X-ray absorption factor exhibited by the alkali-free glass substrate comes to as high as 16.8%. Specifically, the light reaches the scintillator while 15% or more of X radiation with which the photodetecting unit has been irradiated is lost as a result of X radiation being absorbed by the substrate. As mentioned above, when consideration is given to maintaining the performance of the a-Si film, using alkali-free glass for the substrate is indispensable. As a result of X radiation being absorbed by the substrate, a great decline in the amount of X radiation entering the scintillator is unavoidable. Specifically, a high image quality feature that is yielded when the scintillator is exposed to X radiation emitted from the direction of the photodetecting unit is diminished.
Incidentally, if the radiological image detection apparatus not having a substrate in the photodetecting unit can be built, the radiological image detection apparatus will be preferable that absorption of radiation, which would otherwise be caused by the substrate, can be avoided. In Patent Document 2 (JP-A-2009-133837) and Patent Document 3 (JP-A-2008-235649), after a thin film portion, such as a PD and a TFT, has been formed on a substrate, the substrate is peeled off and eliminated. In this case, a panel that is a laminate made up of a scintillator and the thin film portion will become easily deflected under the weight of the scintillator. If the panel remains deflected, clearance will arise between a support member and the panel. When experienced impact, the panel will become rattle, which in turn may inflict damage on the scintillator. In order to prevent deflection of the panel, the support member that supports a subject and the thin film portion must be firmly bonded together substantially in their entirety.
As mentioned above, in order to enhance, to a much greater extent, image quality of the X-ray image detection apparatus of the type in which radiation is emitted from the direction of the photodetecting unit of the scintillator, a radiological image detection apparatus including a substrate-free photodetecting unit is desired. However, if the substrate is separated as described in Patent Documents 2 and 3, the scintillator, the thin film portion, and the support member must be firmly bonded in their entirety in order to prevent occurrence of deflection. If they are firmly bonded in their entirety, replacement of the support member will become difficult. Further, when the support member and the panel are separated from each other, the thin film portion will be damaged. CFRP (Carbon Fiber Reinforced Plastic); for instance, is used for the support member. When a surface of the support member is flawed, fibers are broken, to thus become finely split. The thus-split support member may give discomfort to the patient or be liable to become unsanitary. Flaws in the support member also lead to occurrence of a defect in a detected image. When compared with the support member, the panel is expensive. Discarding the panel every time the support member is replaced is uneconomical. For this reason, replacement of the support member is indispensable. Specifically, easily-separable bonding of the panel to the support member is important.